This invention relates generally to the field of telecommunications switching systems and more particularly to a telecommunications switch that includes resource interface cards for connections, without a loss of network connectivity, to external resources which may provide call processing services.
An example of a switching system to which the present invention applies is described in U.S. Pat. No. 5,544,163, Expandable Telecommunications System, the contents of which are incorporated by reference herein. A telecommunication switching node described therein has line cards with multiple ports connected to subscriber""s telephone lines or to other devices such as PSTN trunks. The switch also includes a CPU/matrix card and at least two system buses for switching calls received on one port to another port in the system. One of these buses is an incoming bus that passes messages from the line cards to the matrix card and the other is an outgoing bus which transmits messages from the matrix card to the line cards. In order to perform switching on calls, the switch receives information from and transmits information to line card ports over the system buses at predetermined times known as time slots. Each time slot generally corresponds with a port on the switch.
Each call involves connection between two ports. Because communication between these ports is bidirectional, it thus requires four time slots on the system buses. One time slot is used for transmission from one port to the matrix card, a second time slot is used for retrieving information from matrix card and sending it to the other port; the other two time slots are used for transmissions in the other direction. The switch stores information received in time slots in the incoming bus in corresponding memory locations. Thereafter, the switch retrieves the information from memory and transmits it over outgoing time slots assigned to the ports that are to receive the information.
In addition to call switching, the switch is also required to provide call processing services including, inter alia, tone generation and detection and voice mail. These services are provided by cards that are connected to the system buses to communicate with the line card ports to which the services are to be provided. A prior system as described in U.S. Pat. No. 5,349,579, Telecommunications Switch with Programmable Communications Services, includes programmable service cards that transmit information directly to the line cards over the outgoing bus, i.e., without passing through the CPU matrix card. Similarly, they receive information from the line cards directly over the incoming bus. Thus only two time slots are needed in these communications as compared with the four time slots that would be used if the information passed through the CPU/matrix card. This reduces the number of time slots required for communications between the ports and the desired call processing services on the services card, thus minimizing the reduction in the call-handling capacity of the switch. The communications services cards described therein service only resources that are internal to the switch, i.e. on cards connected to the switch buses. In order to connect to external voice processing resources, some systems use a Resource Bus Interface (RBI) card that is plugged into the system buses for communications with the various ports. The RBI card is connected to one or more external resources by means of a conventional voice processing resource bus. The card communicates with the line card ports by way of the CPU/matrix card. It thus requires four time slots on the system bus for each call that uses its resources. This ties up line card ports that would otherwise be used for processing calls and reduces the call-handling capacity of the switch.
As described in U.S. Pat. No. 5,544,163, an expandable system comprises a plurality of switching nodes interconnected over an internodal bus. A call between ports on different nodes is routed over the system buses on the two nodes and the internodal bus. A system resource may have more capacity than is needed for one switching node and it would therefore be desirable to make the resource available to the other nodes in the system.
In the present invention a telecommunications switching node includes at least one resource interface card which serves as an interface for connection to external call processing resources. The interface card communicates with the line cards in the switching node directly over the system buses, i.e. without passing through the CPU matrix card and it uses two line card ports to connect to all external resources. The resource interface card also communicates with line cards that are connected to the system buses in other switching nodes in an expanded switching network. Its resources are thus available to ports in the other nodes when those nodes have available ports that are not occupied with other tasks. For communications with the latter ports, the resource interface card transmits information through the CPU/matrix cards on its switching node and on the nodes where the communicating ports reside. Thus for communications with ports on its switching node, the interface card receives information on the incoming bus and transmits it on the outgoing bus and for communications with ports on other nodes it receives information on the outgoing bus and transmits it on the incoming bus.
In the preferred embodiment of the invention, the incoming data from ports in the same switching node as the interface card or from other nodes in the system enter the resource through either the incoming bus or the outgoing bus and it is stored in a memory in the resource interface card. A memory address is read from a transmit connection map, i.e., a lookup table of memory addresses. Data in the memory location identified by that address is then transmitted to an external resource over a resource bus. Once the data is processed by the external resource, information is sent back to the resource interface card for transmission to the appropriate port. The information is stored in a second address in the resource card""s memory. That address is ultimately selected from a receive map and the data in the memory location identified by that address is transmitted on a time slot basis to either the incoming bus or the outgoing bus, depending on whether the receiving port is in the same switching node as the interface card or in another node.